In a conventional butterfly valve type valve device used for opening and closing a passage through which exhaust gas recirculation (hereinafter referred to as “EGR”) gas or the like flows, a seal ring which is mounted in an outer peripheral groove of a valve and seals a gap between an outer peripheral wall of the valve and an inner wall of a passage portion is known.
In the conventional valve device, an environmental temperature of the gas passage portion extends over a wide range from a low temperature in a state left in a cold district to a high temperature exposed to the exhaust gas. In addition, since the materials of the valve, the seal ring, the nozzle constituting the gas passage portion and the like are different from each other, a clearance is set based on considering the difference in linear expansion of each material.
For example, in the valve device disclosed in Patent Document 1, a seal ring made of resin is used in place of a metal seal ring commonly used before that. In the case of using the metal seal ring, an inner circumferential sliding surface of the gas passage portion, which is a mating side of the seal ring, is required to secure hardness by surface treatment or the like for preventing abrasion, whereas it is not necessary in the case of using the resin seal ring. Therefore, it is possible to simplify the abolishment of the surface treatment of the gas passage portion and the like.